1. Field of the Invention
The present invention relates to a method of forming a phosphor layer on a cathode ray tube (CRT) panel and a water soluble emulsion with photosensitivity as an intermediate layer thereof.
2. Description of the Prior Art
In general, a phosphor screen of a color cathode ray tube includes red, green and blue phosphor layers (e.g., phosphor stripes or phosphor dots) formed on an inner surface of a panel and a carbon layer serving as a light absorption layer formed between the respective phosphor layers. A metal-backing layer made of an aluminum vapor deposited film is formed on the surface of the phosphor screen through an intermediate layer that is used to smooth the surface of the phosphor layer. The intermediate layer is evaporated and removed by the succeeding baking process.
Such a color phosphor screen is generally formed as shown in FIGS. 1A through 1C.
Initially, a PVA (polyvinyl alcohol) photosensitive film is coated on the inner surface of a panel 1. Then, using color selection electrodes as masks, it is exposed to three red, green and blue lights and developed to form resist layers made of the PVA photosensitive film of the portions in which respective color phosphor layers, e.g., respective color phosphor stripes are to be formed. After the hard film treatment, a carbon slurry is coated on the whole surface including the resist layers, dried, inverted and then developed to thereby remove the carbon layer together with the resist layers, whereby a carbon stripe 2 is formed on portions located between the respective phosphor stripes which will be formed hereinafter. Then, respective color phosphor stripes 3 [3R, 3G and 3B] corresponding to red (R), green (G) and blue (B) are formed by a slurry method (see FIG. 1A).
An acrylic layer (e.g., acrylic emulsion manufactured under the trade name of PRIMAL B-74, C-72, AC-73 or the like by NIPPON ACRYL KABUSHIKI KAISHA or manufactured under the trade name of LUSITE (acrylic resin is dissolved in toluene) by TOKYO OHKA KOGYO KABUSHIKI KAISHA) serving as an intermediate layer 4 having high smoothing property is coated on the whole surface including the carbon stripe 2 and the phosphor stripe 3 (see FIG. 1B).
Then, a metal-backing layer 5 made of an aluminum evaporating layer is formed on the intermediate layer 4 (see FIG. 1C ). Thereafter, the intermediate layer 4 is evaporated and then removed by the baking treatment, thereby a desired color phosphor screen is formed.
A pitch of earth of the respective phosphor stripes 3 [3R, 3G, 3B] on the phosphor screen is made finer as the color cathode ray tube becomes high in grade and high in definition. As a result, when the PRIMAL (trade name), for example, is used as the intermediate layer 4, the smooth intermediate layer 4 cannot be formed on the surface of the phosphor stripe 3 without difficulty.
That is, since the surface tension of PRIMAL is small, the PRIMAL permeates the phosphor stripe 3 and also the PRIMAL flows onto the carbon stripe 2. Therefore, the smooth intermediate layer 4 cannot be formed. There is then the disadvantage that the brightness of the phosphor screen is lowered.
If the intermediate layer 4 is increased in film thickness, then the smoothing property thereof is improved. In this case, however, during the furnace process, the metal-backing layer 5 is floated, i.e., aluminum is floated (so-called aluminum swell) or aluminum is peeled off.
On the other hand, if the LUSITE (trade name) is used to form the intermediate layer 4, then the smooth intermediate layer 4 is formed. In this case, however, the portion on the carbon stripe 2 is empty so that color purity is deteriorated due to scattering of light, a reflected electron or the like.